BACKGROUND OF THE INVENTION
The present invention relates to fasteners in particular screws and bolts having a head provided with a recess to receive a driving tool for turning the screw or bolt.
GB-A-1150382 appears to be the first disclosure of a screw provided with a multi-tiered recess and a corresponding multi-tiered driver. GB-A-2285940 discloses essentially the same idea. Both these publications describe the advantages provided by the arrangements disclosed. The first is that the recesses are essentially parallel-sided and consequently eliminate cam-out problems that are associated with cross-head recesses. Secondly, they give the possibility of a single driving tool being suitable for driving a wide range of screw sizes.
The single driving tool typically has three (for example) tiers of driving surfaces which are employed to drive large screws having three tiers of recess. However, the same tool can be employed with smaller screws having only two tiers of recess, the largest tier being omitted. Indeed, even smaller screws may have only one, the smallest tier, in their recess and be driven by the smallest tier only of the tool.
GB-A-2329947 discloses a similar arrangement, and WO-A-0177538 discloses tiers that have such a small extent in the recesses of screws and bolts that, at the torques at which the screws are intended to be operated, they cannot be turned unless at least two tiers are both engaged by the tool. Otherwise, the screw is arranged to round out of engagement with the driving tool. This provides a security feature in that only the appropriate tool will undo the screw.
However, until co-pending application GB0124122.3 was filed by the present applicant on 8 Oct. 2001, these ideas were not a practical reality, because the recesses could not competitively be formed in screws and bolts.
Now, interest is developing in such fastening systems. However, the system so far has primarily been applied only to the smaller wood and machine screws, that is to say, No.6- to No.10-size wood screws (ie about 2 mm to 5 mm diameter—lengths about 15 mm to 100 mm) and M2 to M10 machine screws (ie 2 mm diameter threads to 10 mm). However, there is a need, particularly in the machine screw and bolt field, for larger sizes.
In principle, there is no limit to the number of tiers that can be included or added to a recess or driver. But there comes a point when the driver, if it is big enough and strong enough to drive the largest screws and bolts, it will be far too awkward, bulky and heavy to sensitively drive the smaller screws. Moreover, in larger screws, the torque transmission capability of the smaller tiers becomes insignificant.
Consequently it is desirable to divide the system between ranges of sizes of screw/bolt, but, in so doing, some of the benefit of the system is lost, because at least two tools then become necessary to cover the entire range of sizes.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a system that mitigates this loss of universality.
In accordance with the present invention there is provided a fastener system comprising a plurality of ranges of size of threaded fastener, each fastener having a head provided with a recess to receive a tool to rotatingly drive the fastener, and wherein:
in each range of sizes, the largest size of fastener has a recess comprising a plurality of driving tiers of reducing size superimposed on one another, each tier having sides which are substantially parallel a long axis of the fastener and define a polygon in section;
between two adjacent size ranges, there is a common tier, being the largest tier of the recess of the smaller size range and the smallest tier of the recess of the larger size range, which common tier is the same section in each range; and
the depth from the base of the largest recess to the base of the smallest recess in the smaller size range is less than the depth of the smallest recess in the larger size range.
Preferably, there are two size ranges of fasteners comprising screws of diameters from about 2 mm to about 10 mm and from about 10 mm to about 30 mm. The screws may be size M2 machine screws to size M10 in the small range and size M12 to M30 in the large size range.
The common tier is preferably hexagonal in section, but it equally could be pentagonal or some other straight-sided polygon.
The common tier preferably has a diameter of about 6 mm, preferably 5.9 mm.
The smaller size range of fasteners may have three tiers in larger fasteners, two tiers in middle size fasteners, and one in the smallest fasteners. The larger size range may have four tiers in the larger fasteners, and three tiers in smaller fasteners. Of course, smaller fasteners in the larger size range are going to be bigger than larger size fasteners in the smaller size range, unless it is desired that there might be screws of the same dimension, some having recesses in common with the larger size range of fasteners, and some having recesses in common with the smaller size range of fasteners
By this simple expedient, then, of a common tier between the two size ranges, a driver adapted for the smaller size range can be employed to drive the larger size of fasteners, and vice versa. This is a very useful feature because it is frequently the case that either of the following events occurs:
a) A user spends some time aligning objects to be joined by a fastener and, when aligned, holds them in place while a fastener is inserted. Then, he/she reaches for the tool to drive the fastener, only to find that the wrong driving bit is fitted in the tool! As a result, often the entire workpiece has to be dismantled while the user fits the right bit to the tool (or finds the right tool) before starting again.
b) One of the benefits of the fastening system to which the present invention relates is that, because the recess is parallel-sided, there is no cam-out. Consequently, it is possible to fit a fastener onto the end of the tool without the fastener immediately falling off. This is useful because, often, access to the location where the fastener is to be applied is restricted or confined. Being able to manoeuvre a fastener into position with the aid of the driving tool frequently facilitates this task.
With the present invention both situations can be accommodated conveniently. In the first case, either a small driver can initiate the connection of the fastener (from the larger size range), or, indeed, a large driver can initiate connection of a fastener from the smaller size range, (as long as that fastener has the largest size recess provided for that range). Clearly, with the wrong driver it is not advisable to attempt final tightening, but that is not the issue. Once the fastener has been sufficiently engaged, the right driver can be found and applied for final tightening of the fastener.
As for event b) above, employing the driver to position fasteners in a workpiece does, indeed, frequently facilitate connection. However, the problem is not assisted as much as it might be when the proper driver is used. With larger sizes, the driver is often no slimmer than a user's own fingers, for example. However, by using the driver appropriate for a smaller range of fasteners to locate and begin driving of a fastener from the larger range, easier and quicker engagement of the workpiece is likely.
In the machine screw field, it is found that a single driver is capable of driving all screws in the range M2 to M10. M2 screws typically require no more than about 0.3 Nm of torque to be applied, and a single 2.5 mm diameter, 1.5 mm depth, driving tier is found adequate. M10 screws typically require about 70 Nm, and three tiers, or at least two larger tiers, are necessary to transmit this torque. The largest tier typically might have the dimensions mentioned above for the smallest tier; 4 mm diameter, 1 mm depth for a middle tier; and 6 mm diameter, 1.5 mm depth for the largest tier.
However, for bolts in the range M12 to M30, a driver tool of 6 mm diameter is not adequate to transmit the torques expected, namely about 130 Nm for M12, and about 2000 Nm for M30. Hexagonal bar of the grade steel from which drivers are typically made will shear at about 150 Nm torque.
Nevertheless, the benefit of the multi-tier system can still be experienced with an upgraded tool but, in practice, it is found best not only to increase the overall size of tiers, but also to provide four of them. Preferably, the tiers should have about 6, 10, 14 and 19 mm diameters, and each about 2.5 mm depth.
The largest diameter tier is ideally considerably deeper.
The tiers can have any non-circular section (by which “polygon” and “polygonal”, as used herein, are broadly meant) and each tier may be the same or different, aligned or offset, either rotationally, axially or both. The term diameter used herein is therefore imprecise and is merely for approximate guide. With reference to a hexagonal profile, the diameter referred to is flat-to-flat.
In this first aspect of the present invention, there is also provided a set of punches having tier-forming sections for forming the recess of fasteners of the fastening system as defined in this first aspect, said set including one punch for a smaller size range of fasteners that has a largest tier-forming section of a common section, and another punch that has a smallest tier-forming section of the same common section.
A different problem, on the same theme as that addressed by the first aspect of the present invention, is that, even in a given size range such as M2 to M10 as described above, at least at size M10 there is a potential gap between the driver's capability and the required torque. The solution is to embed the recess further into the head of the fastener. This is possible because the head is inevitably bigger on larger screws and bolts. Embedding the recess further creates more torque transmission area of the largest diameter tier of the driver, and consequently the greater torques can be transmitted.
However, two issues arise. Firstly, in the automotive industry in particular, anti-corrosion lacquers are generally applied to bolts. This lacquer can fill the smallest recess tier and prevent proper and complete engagement of the driver into the recess, at least with normal hand pressures applied to the driving tool, and especially with deep recesses. Secondly, the deeper a punch is driven into a screw head to form the recess (in the cold-forming process employed) the more likely it is that the tip of the punch (forming the smallest recess tier) will snap-off, in time.
Accordingly, it is an object of the second aspect of the present invention to provide a system that solves these problems, or at least mitigates their effects.
In this aspect, the present invention provides a fastening system for a range of different sizes of fastener in which each fastener is provided with a recess to receive a tool to rotatingly drive the fastener, wherein:
the tool has at least three tiers of driving section at its end, each tier comprising sides disposed substantially parallel a long axis of the tool and forming a polygon in section, the tiers becoming progressively smaller in section near the end of the tool; and
the range of fasteners to be driven by the tool includes a first fastener whose recess is shaped to be drivingly engaged by at least the third and second smallest tiers of the tool, but not the smallest tier, the recess receiving the second smallest tier of the tool being deep enough to accommodate the smallest tier without any driving engagement therebetween, and without preventing full engagement of said second and third tiers in the corresponding tiers of the recess in the fastener.
The range preferably includes a second, smaller fastener whose recess is shaped to be driven by the smallest, and the second and third smallest, tiers of the tool, wherein:
the recesses of the first and second fasteners are such that the depth of engagement of the third smallest tier of the tool in the recess of the second fastener is less than the depth of engagement of the third smallest tier of the tool in the recess of the first fastener.
The range of fasteners may comprises screws of diameters from about 2 mm to about 10 mm. Indeed, the screws may be size M2 machine screws to size M10. In this event, said first screw may be M10 and said second screw may be M8.
The recesses of the first and second fasteners are preferably such that the depth of engagement of the third smallest tier of the tool in the recess of the second fastener is about 1 mm and the depth of engagement of the third smallest tier of the tool in the recess of the first fastener is about 3 mm. The third smallest tier may have a diameter of about 6 mm, preferably 5.9 mm.
In this second aspect, a set of punches is also provided, having tier-forming sections for forming the recess of fasteners of the fastening system as defined in this second aspect, said set including a first punch for a smaller size of fastener and that has three tier-forming sections, and a second punch for a larger size of fastener and that has two tier-forming sections, wherein:
the larger tier of the second punch has the same section as the largest tier of the first punch; the smaller tier of the second punch has the same section as the middle sized tier of the first punch; and
the length of the smaller tier of the second punch is the same or longer than the combined depth of the middle sized tier and smallest tier of the first punch.
Consequently, this aspect of the invention does away with the smallest tier of recess in the largest fasteners, opening it out, preferably, into an extension of the second smallest tier of the recess. The depth is maintained, of course, to permit full entry of the tool.
This measure then, does not significantly adversely affect the torque transmission. Indeed, on the larger screws, the torque transmission by the smallest tier is de minimis when compared with the more deeply embedded, largest tier. Instead, it reduces punch breakage and it prevents incomplete engagement of the tool with the recess of the fastener. Nor does it affect the use of the same driving tool on smaller sizes of screws that are provided with the small recess tier, so that this aspect of the system is not impaired.